The present invention relates to a method and a device for controlling an internal combustion engine.
A method and a device for controlling an internal combustion engine are known from German Patent 197 12 143. In the mode of operation described there, the fuel injection of one cycle is divided into a first partial injection and a second partial injection. In this context, the rail pressure, which is used for calculating the duration of the main injection, is corrected as a function of the duration of the pre-injection and of the interval between the pre-injection and the main injection.
In common-rail systems of this type, pressure fluctuations occur after every injection. The quantity of fuel injected during the main injection is fundamentally a function of the fuel pressure in the main injection. Fluctuations in the fuel pressure result in fluctuations in the quantity of fuel injected.
The present invention is based on reducing the influence of pressure fluctuations on the quantity of fuel injected.
As a result of the fact that in the second partial injection a fuel-quantity variable characterizing the quantity of fuel injected in the second partial injection can be corrected as a function of at least one pressure variable, which characterizes the fuel pressure, and of the fuel quantity variable, the influence of the subsequent partial injection on the subsequent partial injection can be significantly reduced. In a common-rail system, as a pressure variable, the rail pressure is preferably used. As a fuel-quantity variable, a fuel quantity to be injected, a drive duration for a corresponding actuator, or another variable characterizing the fuel quantity to be injected can be used.
A further reduction of the influence of the two partial injections on each other can be attained if, in addition, the fuel-quantity variable can be corrected as a function of an interval between the two partial injection and/or of a temperature variable. In this context, the interval between the actual injection end and the actual injection beginning can be used. Alternatively, the interval between the drive end and the drive beginning can be taken into account. Furthermore, it is also possible to have recourse to variables characterizing the interval between the partial injections.
It is particularly advantageous if the fuel-quantity variable, corrected in this manner, is limited to a minimum value. This means that if the fuel-quantity variable is smaller than a minimum value, then the minimum value is used as the fuel-quantity variable.
The minimum value is preferably specifiable at least as a function of the rail pressure and/or of the interval between the two partial injections.
It is particularly advantageous if this correction takes place after a further correction, using a quantity-balancing regulation. As a result of the sequence of corrections, the two corrections are prevented from influencing each other in an undesirable manner.
Due to the fact that the correction is only carried out in certain operating states, it is achieved that the correction only takes place in those operating states in which the two partial injections influence each other, or in which the correction is effective.
The correction is arrived at in a particularly simple manner as a result of the fact that a basic value is determined as a function of at least the pressure variable and/or the interval between the two partial injections, that a weighting factor is determined as a function of at least the fuel-quantity variable, and that the correction of the fuel quantity to be injected takes place as a function of the basic value, which is arrived at using the weighting factor.